1. Field of the Invention
The present invention relates to a motor, and more particularly to an armature structure of the motor.
2. Related Art
The armature core of a conventional motor is illustrated in FIG. 11(a). As shown, the armature core includes a plural number of salient poles 114. Those poles are radially extended from the center of the armature core, and each of the salient poles includes an arm 116 and an arcuate head 117 extending to both sides at the extreme end of the arm. An open slot 100 is present between the adjacent salient poles 114. A coil is wound on the arms of the salient poles 114 through the open slots 100. Specifically, a conductive wire is wound on the arms 116 of the salient poles 114 in a manner that the armature core 11 is moved relatively to and around a nozzle which guides and feeds the conductive wire. In this case, the width W of the opening of each open slot 100 is sufficiently wide so as not to hinder a smooth movement of the nozzle by the arcuate heads 117.
However, if the opening width of each open slot 100 is too narrow as shown in FIG. 11(b), the nozzle is limited in its movement for winding the drive coil 17. The limited movement of the nozzle creates the following problems. The winding of the drive coil 17 around the arms 116 is not uniform. That is, the wound coil layer is thicker toward the extreme end of each arm 116, and forms dead spaces D near to the roots of the arms 116, as shown. The presence of the dead spaces D reduces the number of turns of the wound drive coil 17, and possibly gives rise to a problem that the resultant wound coil layer is easy to get out its shape and in turn to loosen the wound drive coil 17.
To secure the properly winding of the drive coil 17, it is desirable that the opening widths of the open slots 100 are enough wide. However, the wide opening width creates another problem of degradation of the output characteristic of the motor. In a case where the opening present between the adjacent arcuate heads 117 is large, a magnetic flux density is considerably reduced in the openings, and a reluctance of the magnetic circuit including the openings is remarkably increased. The result is that a large cogging occurs in the motor, and the motor loses its smooth continuous rotation.
The technique in this field has been unable to solve the following antinomic problem; when the end of properly winding the drive coil 17 is achieved, the end of smoothing the motor output is lost, and vice versa.